ABS Diagnostic Project - How ABS sensor works?

I completed a project about anti-lock breaking systems two weeks ago. In order to have solid knowledge, it is always needed to read articles, looking at similar projects before and during development stage. I can say that there is no similar published projects on web. Therefore I needed to write this note series to contribute open source world. I know that this is not really big contribution but it is what it is. 

Let's start.

ABS sensor on wheel allows vehicle to determine number of rotation in a curtain time. There are different types of ABS sensor structure in the market. As some of them utilize magnetic tone wheel, others might use classic tone wheel to calculate rotation. In fact, we only need to know sensor output values such as how many pulse does sensor generates in one rotation, which voltage or current represent bit 1 and bit 0 in the sensor output etc.. In the end, all we need to do is counting this 1 and 0 for one rotation in certain time.

 

For instance, assuming we have an ABS sensor which generates 50 pulses from sensor output in one rotation. If we count 40 pulses in 2 sec, what would be the angular speed?

   Angular Speed = ∆Angle / ∆Time

ω = ∆ɸ / ∆t

If 50 pulses = 2╥, what would 40 pulses = ?

40 pulses = 1.6╥

ω = 1.6╥/2

ω = 0.8╥ rad/sec

Basic math right?

My ABS sensor generates 10mA for bit 1, 5mA for bit 0. It also generates 72 pulses in one rotation.

      What is the project scope?

Project I have realized is about testing ABS sensor to see if it works fine or produce wrong signal in rotation. It is crucial to have this kind of quality control since any failure can cause fatality.

      Why/How does ABS sensor generate wrong signal output?

We said that ABS sensor should generate certain amount of signal in one rotation depending on intertnal structure. Assume that one of tone wheel tooth is broken, sensor generates one less pulse than what should be. Or if one of tooth is bent, we will have similar problem.

After a while your ESP or ABS light will on in your instrument cluster. This would be the best case failure scenario.

Now, question is that how do you ensure that your part is perfect before sending it to your customer?

We are going to find a solution next article.